The UPSC exam pattern transitions from Preliminary to Mains primarily in terms of format and focus. The Preliminary Examination comprises multiple-choice questions (MCQs) aimed at assessing a candidate's knowledge base, while the Mains Examination involves descriptive answer writing, testing analytical abilities and comprehensive understanding. The mains consist of nine papers, including General Studies, optional subjects, and an essay paper. The interview stage follows the mains, serving as the final assessment of candidates’ suitability for civil services. This progression ensures evaluation of both theoretical knowledge and practical application.